Health impact assessment of Philadelphia's 2025 tree canopy cover goals

Background Cities across the world are undertaking ambitious projects to expand tree canopy by increasing the number of trees planted throughout public and private spaces. In epidemiological studies, greenspaces in urban environments have been associated with physical and mental health benefits for city dwellers. Greenworks Philadelphia is a plan to increase tree cover across Philadelphia (PA, USA) by the year 2025. We aimed to assess whether an increase in tree canopy or greenspace in Philadelphia could decrease mortality. Methods We did a greenspace health impact assessment to estimate the annual premature mortality burden for adult residents associated with projected changes in tree canopy cover in Philadelphia between 2014 and 2025. Using up-to-date exposure–response functions, we calculated the number of preventable annual premature deaths city-wide, and for areas of lower versus higher socioeconomic status, for each of three tree canopy scenarios: low, moderate and ambitious. The ambitious scenario reflected the city's goal of 30% tree canopy cover in each of the city's neighbourhoods; and low and moderate scenarios were based on the varying levels of plantable space across neighbourhoods. Findings We estimated that 403 (95% interval 298–618) premature deaths overall, including 244 (180–373) premature deaths in areas of lower socioeconomic status, could be prevented annually in Philadelphia if the city were able to meet its goal of increasing tree canopy cover to 30%. Interpretation Bringing all of Philadelphia, and particularly its poorer neighbourhoods, up to the 30% goal of tree canopy cover is not without challenge. Nevertheless, policies are warranted that value urban greening efforts as health-promoting and cost-saving measures. Funding Spanish Ministry of Science, Innovation and Universities, and Generalitat de Catalunya